I was told by both Rough Country and Jeep (DC) the springs in all TJ's (ie; 2003 - 2006) are the EXACT SAME SPRING. Check the part numbers for a 2004 Rubi and 2004 X. Their the same. Where the difference is is in the axles. The D44's front & rear on a Rubi sit 1/2" higher than axles on a Sport or X model.
For example, if you were to buy a 2.5" lift from Rough Country, on the Sport and X models, you will achieve 2.5" of lift, where as on the Rubi, you only get 2.0" lift due to the axles - not the springs.
Oh and as for the OP's question -- You can't appreciate the "specs", until you've wheeled a Rubi off road!
I went through and reread what you have had to say. Here is your first comment, which makes no sense at all. And BTW the last two pages of this thread have been a total thread hijack.
Anyway, as you explain it, the rubi axles sit 1/2 higher and that causes you to lose 1/2 of lift. How do you figure this? You would gain 1/2 inch using that ideology, but in actuality, you neither gain, nor lose lift due to the axle size. If the axle sits 1/2 higher, so do the coil buckets that the coils sit in. If the spring is "X" height, then your upper coil bucket will sit that distance from the bottom. You would still net 2 1/2 inches of lift. Your rig will sit 1/2 higher than a Sport, or X model.
I have owned two Rubicons and done extensive work with my axles and know how all this works. I am currently putting Dana 60 axles under my Jeep and we all know these are much bigger than D44s. Had I chose to keep my Rubicon Express 5.5 lift coils, my rig would sit 5.5 inches from the axle coil buckets. In order to keep my COG and ride height down, I had to use 4 inch springs to compensate for the larger mass of the D60.
When Rough Country told you the X and Rubicon coils where the same, they were talking about size. They are identical except the spring rate when they come from the factory. All the coils that RC sells with that kit are identical, as are most other lift manufactures. There are a few that will give you different spring rate choices, but most of the lower end stuff is all the same. Regardless, your axle size is not going to reduce the amount of lift the spring provides. It still sits in coil buckets and still fills the space between point "A" and "B".